Types of transformer fluid tests
Types of testing
|Transformer routine insulating fluid tests:||Routine lube oil/hydraulic fluid tests:|
|Dissolved Gas Analysis (DGA)||Viscosity at 40°C|
|Screen or physical properties||Acid / Base Number|
|Dissolved Moisture||ICP-AES Spectroscopy|
|Optional tests for further investigation||Particle Count|
|Furan / Methanol||Fourier Transform infrared Spectroscopy (FTIR)|
|Particle count||Ferrous Density|
|ICP-AES Spectroscopy||Membrane Patch Colormetric (MPC)|
|Fire point||Linear Voltammetry for Additive Content|
Screen testing evaluates the physical, electrical and chemical attributes of the transformer oil. Each test is an indication of how suitable the insulation liquid is for service. HSB’s screen tests include: Dielectric breakdown, Power factor, Interfacial tension, Acidity, Color, Specific gravity.
Dielectric breakdown measures the breakdown voltage of an insulation liquid. This test also serves as an indicator of the presence of other contaminating agents such as sediment, moist paper fibers and conducting particles. ASTM D-877 was the method of testing dielectric breakdown until recently. The ASTM D-1816 uses rounded probes at a specific gap with a stirring action to produce results that are more sensitive to moisture and particle contamination. The D-1816 can produce lower breakdown voltage results that may still be within standard guidelines.
Power Factor measures the amount of energy dissipated as heat. This test helps reveal the quality and integrity of the insulating liquid and can be used to determine when a filtering or change of transformer liquid is needed. The power factor of overheated or contaminated insulating fluid will increase and can give the based for additional investigation.
Interfacial tension determines the presence of polar compounds, which are considered to indicate oxidation contaminants or deterioration from the transformer construction materials. Elevated moisture content will reduce the insulating fluid IFT and may indicate the need for fluid processing.
Acidity measures the acid levels in the transformer liquid. As acid levels increase, the quality of the oil decreases, causing dielectric loss, corrosion, and thermal problems from sludge.
Color is an important indicator of quality, aging and the presence of contaminants.
Specific gravity verifies the weight to provide the type of insulating fluid.